Circuit breaker



1954 J. G. JACKSON ETAL 2,697,151

CIRCUIT BREAKER Filed Sept. 16, 1952 3 Sheets-Sheet 1 Dec. 14, 1954 CIRCUIT BREAKER Filed Sept. 16, 1952 3 Sheets-Sheet 2 J. G. JACKSON ETAL 2,697,151

1954 J. G. JACKSON EI'AL 2,697,151

United States Patent CIRCUIT BREAKER John G. Jackson, deceased, late of Detroit, Mich., by

Jean E. Jackson, executrix, Detroit, and Ralph H. Kingdon, Birmingham, Mich., assignors to Square D Company, Detroit, Mich., a corporation of Michigan Application September 16, 1952, Serial No. 309,862

22 Claims. (Cl. 200-116) This invention relates to apparatus for making and breaking electric circuits, and more particularly to an electric circuit breaker manually operable for switching operation and automatically operable to break the circuit in response to current overload.

An object of the present invention is to provide an im- Another object of the present invention is the provision of an automatic electric circuit breaker having novel ambient temperature compensating means.

Another object of the present invention is the provision of a circuit breaker having a bimetallic member which has a fixed and a free end, a movable contact carrying arm being fixedly mounted to the free end of the bimetallic member, a resilient latch being provided for engaging the contact carrying arm and retarding its movement from a first to a second operating position, the latch being releasable upon the application of sufiicient force to the contact arm by either the bimetallic member or a manually operable handle.

Another object of the present invention is the provision of a circuit breaker in accordance with the preceding object in which means are provided for engaging the handle to prevent undesired movement of the contact arm from the second to the first operating position.

Another object of the present invention is the provision of a circuit breaker in accordance with the preceding objects in which the bimetallic member carries a spring which engages the manually operable handle when held in on position to prevent automatic reclosing of the circuit.

Another object of the present invention is the provision of a circuit breaker of improved design having a main and a second bimetal in which the second bimetal movement is in the opposite direction to the movement of the main bimetal upon change in ambient temperature, and in which the second bimetal directly opposes movement of the main bimetal with a force determined by the ambient temperature to correct for the effect thereof on the main bimetal.

Other objects and features of the invention will be readily apparent to those skilled in the art from the specification and appended drawings illustrating certain preferred embodiments in which:

Figure 1 is a side elevational view of the circuit breaker of the present invention with the side cover broken away to show the internal parts in the normal on position.

Figure 2 is a view similar to Figure 1 in which the parts are shown in normal off position.

Figure 3 is a partial view similar to Figures 1 and 2 in which the parts are illustrated in the position assumed when the handle is maintained in the on position during overload current flow and the main bimetal has cooled suiiiciently to urge the movable contact toward the on position.

Figure 4 is a partial sectional. view along the plane of line IV-IV of Figure 1.

Figure 5 is a partial sectional view along the plane of line V-V of Figure 1.

2,697,151 Patented Dec. 14, 1954 Figure 6 is a partial side elevational view of a first modification of the present invention.

Figure 7 is a sectional view along the plane of line VIIVII of Figure 6.

Figure 8 is a partial view similar to Figure 3, showing a modified form of one aspect of the present invention.

Figure 9 is an enlarged plan view of the latch employed in the embodiment illustrated in Figures 1 through 5.

Figure 10 is an enlarged partial sectional view along the plane of line X-X of Figure 9.

The circuit breaker of the present invention is of the general type illustrated and claimed in application for Circuit Breaker, filed March 24, 1951, Serial No. 217,330 now Patent No. 2,666,114 dated January 12, 1954.

Figure 1 illustrates the device of the present invention with the parts in the normal on position. As shown therein, the device comprises a box-like base 1 of insulating material, having an open side which is normally closed by a flat cover piece 2 also of insulating material, the cover piece 2 being attached to the base 1 by suitable means such as spun-over rivets. Integrally molded into the base 1 are a plurality of recesses of three sides, one of these sides being the back wall of the base 1. Into one of these recesses, at the left of Figure 1, there is pressed a terminal member 3 having an end 4 which projects beyond one end wall of the base 1 and receives there a terminal screw 5. To the other end of the terminal member 3 there is welded a main bimetal 6, the high expansion side of which forms the upper surface as viewed in Figure 1. To the other end of the main bimetal 6 there is welded a movable contact arm 7, having a return bent loop portion 8 near the bimetal 6, and carrying a movable contact 9 at its free end. The arm 7 is formed of a resilient spring strip and is strengthened by a stiffening rib over that portion between loop 8 and contact 9 to rigidify the same, while the loop portion 8 is not so stiffened so that it is readily deformed against its inherent resilience.

Disposed so as to cooperate with the movable contact 9 is a fixed contact 11 which is welded to a contact terminal 12, fitted into suitable recesses molded into the base 1. Terminal 12 has a projection 13 which protrudes through a recess in the bottom of base 1, the projection 13 and a jaw spring 14, which is also positioned within a base 1 recess, serving to provide for resiliently clamping the breaker to a bus bar. Spaced from the cooperating members 13 and 14 an amount equal to the spacing between adjacent bus bars employed with the circuit breaker is a noncurrent carrying bus jaw 15 which is fitted into a base 1 recess, and which has dependent resilient arms which, in the mounted position of the circuit breaker, help hold it in position upon the bus bar structure, this bus jaw 15 being in no Way connected to any of the current carrying parts of the circuit breaker.

To the free end of the main bimetal 6 there is welded a magnetic armature plate 16 having an upturned flange 17 at its free end. Mounted to plate 16 is a spring 18 having a pair of upstanding portions 19 and 21. Rotatably mounted upon a pivot pin 22 integral with the side of base 1 is a manually operable handle 23, the handle 23 being biased to the position illustrated in Figure 2 by a handle spring 20. In the undersurface of handle 23 there is provided a slot 24 having a pair of camming sides 25 and 26 as shown in Figures 2 and 3. The undersurface of handle 23 is also provided with an additional camming surface 27 and an integral shoulder 28, the purpose of which will be subsequently explained.

Referring to Figures 1 through 5, there is mounted on base 1, with its legs embracing contact arm 7, a re silient latch member 29, shown in cross-section in Figure 4. Latch member 29 is provided with a pair of legs 31 and 32, leg 31 being substantially straight but curved slightly transversely to present a smooth line surface to arm 7, as shown in Figure 5. Leg 32 is provided at its upper extremity with an offset portion 33 which is bent from the main portion of the leg 32, and centrally located along the line of bend is a short, coined nub 34 having a sharp corner which projects slightly from the line of bend. The bight 35 of the latch member 29 is, as will be seen in Figure 4, concave in crosssection.

Mounted within a suitable recess in the base 1 is a yoke 36 of magnetic material which is of cross-sectional U shape, the yoke 36 having an end extension 37 of reduced width which projects between the legs of latch 29 and rests upon the concave bottom surface 35 thereof. Threaded into a suitable aperture in the bottom surface of the yoke 36 is an adjusting screw 38 which is fitted into a recess in base 1, and which is accessible when jaw spring 14 is removed. As will be seen from an inspection of Figure 4, rotation of the adjusting screw 38 will vary the position of the extension 37 and hence the concavity of the bight 35 of the latch 29. As the concavity of the bight varies, the inherent bias of the latching legs will vary inversely therewith to vary the forces required to be exerted by contact arm 7 to efiect movement of contact 9 to oif position.

Disposed within a suitable recess in the base 1 is an ambient temperature compensating bimetal 39, one leg 41 to which is secured to the base 1 while the other leg 42 thereof is free.

As shown in Figure l, the bimetal 39 is so constructed and arranged that at normal ambient temperatures when the circuit breaker is in its closed position the leg 42 thereof will not engage the main bimetal 6. Bimetai 39 is so disposed that the high expansion side thereof forms the inner surface, so that upon increase in ambient temperature the legs 41 and 42 of the bimetal 39 tend to spreadapart. Where leg 42 engages bimetal 6 to oppose movement thereof, and the force of opposition will vary with the value of the ambient temperature.

In Figures 6 and 7 there is illustrated a modification of the device of the present invention in which parts similar to those illustrated in Figures 1 through 5 are designated with the same numerals. As will be seen from a consideration of Figure 7, a difierently shaped contact arm 43 is provided which has a looped portion 40, however, similar to that of looped portion 8 described in connection with Figures 1 through 5. Arm 43 cooperates with a modified latch 44 having a pair of similar legs 45, near the extremity of each of which there is provided an offset portion 46. Portions 46 are bent from the main portions of the legs 45, as illustrated in Figure 7, and each of legs 45 is provided with a nub 47, similar to nub 34. As will be seen from Figure 6. there is disposed in a suitable recess in the base 1, a stationary arc barrier 48 having a central opening 49 therein through which the contact arm 43 extends. A separate, movable arc barrier 51 is mounted upon the contact arm 43 so as to be movable therewith.

It will be readily seen that the assembly of the parts into the base is an extremely simple operation which comprises merely fitting the parts into their allotted positions in base 1 and afiixing the cover 2 to the base to close the open side of the base. Portions 50 are provided which are molded integrally with base 1, and the terminal members, when forced into their respective openings, shear oif the tops of portions 50 so that the termin l members are held tightly in position. After assemblv, the bimetal 6 and the contact arm are given an initial set so that they will move the contact 9 to the closed circuit position. In other words, the initial bias of bimetal 6 and the contact arm causes the contacts 9 and 11 to engage. sure between the contacts is supplied through the bias of the latches 29 and 43 operating through the upper, offset portions thereof on the under edges of the contact arm, as shown in Figures 4 and 7. This ressure is increased as enerav is stored in the resilient looped portions (8 or 40) rior to both manual and automatic tripping as hereinafter described. For any given design of the breaker as to size and material, it will be determined h t force it is necessary to exert at the free end of bimetal 6 to effect'opening movement of the contact arm at the desired currentrating. In calibrating the breaker. this force is applied to'the free end of the b metal 6 and the screw 38 is adiusted to vary the position of the pro ection 37 and, hence, the concavity of the latch until the proper bias is placed on the latch legs to release the contact arm at the predetermined pressure and. hence, atthe desired current rating.

n Figure 8 there is illustrated a modification of one aspect of the present invention, those parts illustrated in Figure 8 which'are the same as those which appear The operating contact presin Figures 1 through 5 being similarly numbered. In Figure 8 there is illustrated the main bimetal 6 having the contact arm afiixed thereto, the magnetic plate 16 having one end also afiixed to the bimetal 6. Mounted to the magnetic plate 16, as by welding, is a generally L-shaped spring 52 which, when handle 23 is held in on position during and following automatic tripping, will engage the cam surface 28 of handle 23 to prevent automatic reclosing of the circuit through the circuit breaker as the bimetal 6 cools.

Tlhe operation of the circuit breaker will now be descriwed:

The parts are shown in Figure 1 in closed circuit or on position. In this position, cam 25 of handle 23 is biased by handle spring 20 into engagement with portion 19 of spring 18. The offset portion 33 of the latch 29 engages the underside of the contact arm 6, biasing it upwardly. To open the circuit, handle 23 is rotated in a counterclockwise direction. The initial force exerted on handle 3 in this direction is transmitted through camming surface 25 to portion 19, causing deformation of the spring 18. Portion 19 assumes a slanted position and engages flange 17 of plate 16 to force it downwardly upon continued movement of handle 23. The movement of plate 16 is transmitted to the free end of bimetal 6 which, in turn, moves the end of the contact arm attached thereto downwardly. Inasmuch as the looped portion of the movable contact arm is relatively resilient and the remainder of the contact arm relatively rigid, there is a stressing of the looped portion and a partial rotation of the movable contact arm about the offset portion (33 or 46) of the latch (29 or 44) as a fulcrum. Movable contact 9 is urged more strongly against the fixed contact 11 as this partial rotation occurs. The pressure applied to the movable contact arm will be increased until such time as the offset portions are no longer able to hold the movable contact arm. It will be seen that the contacts are therefore inherently opened at the moment of maximum pressure, thus minimizing burning of the contacts. When this condition is reached, the legs of the latch (29 or 44) are forced apart and the contact arm will be moved with a snap action, resulting from the rapid release of the energy restored in the looped portion (8 or 44)), to the open circuit position. As the contact arm passes below the coined nubs (34 or 47) spring 18 moves below the end of cam side 25 whereupon handle 23 is rotated under the bias of handle spring 20 to the position illustrated in Figure 2. As will be seen from that figure, in this position cam 27 of handle 23 is engaged by the upper surface of spring 18 and serves to hold the movable contact arm in the open circuit position, the latch itself retarding movement of the contact arm only to the extent of the frictional force exerted by the latch on the sides of the contact arm.

To move the parts from the off position of Figure 2 to the on position of Figure I, handle 23 is rotated in the clockwise direction. In this movement, cam 27 rides along the upper surface of spring 18, and shortly before cam 27 leaves spring 18, cam side 26 engages portion 21 of spring 18 moving it inwardly. This movement of portion 21 is necessary as the distance between the outwardly facing surfaces of portions 19 and 21 is greater than the width of slot 24. Further movement of the handle 23 in this clockwise direction then permits the device to assume the position of Figure l, the bias of the bimetal 6 and the contact arm 7, inherent and as exerted by offset portion 33 of latch 29, effecting this closing operation with a snap action. The contact arm, when in on position, continues to be enga ed b the offset ortion of the latch and is bias d upwardl berebv.

With the parts in the position of Figure 1, if handle 23 is rotated clockwise, it is apparent that cam side 25 will be disengaged from portion 19 of spring 18. When this occurs. that component of force transmitted by handle spring 20 which tends to force bimetal 6 toward the off position will be removed. Cam side 26, however, will. by that movement, be forced against portion 21 of spring 18, and thereby tend to restore an opening force to bimetal 6 whereby the calibration of the breaker will remain substantially unchanged.

With the parts in the on position, should a sustained overload occur which is of a magnitude to cause the main bimetal 6 to be sufficiently deflected, the end of the bimetal 6 connected to the end of the movable contact arm will cause, initially, a partial rotation of the contact arm as previously described, until the resilient looped portion of the contact arm is sufficiently stressed to effect a snap opening movement of the movable contact. Handle 23 will then be moved in a counterclockwise direction under the bias of handle spring until the parts assume the position of Figure 2.

With the circuit breaker in the on position, should a heavy overload current through the circuit breaker occur, the flux emanating from such overload current will cause the magnetic armature plate 16 to be attracted to the core 36, the resulting force upon the contact arm tending to effect a snap opening of the movable contact 9 away from the fixed contact 11 in a manner similar to the opening on manual operation and on bimetal flexure through heating alone.

With reference to Figure 3, there is illustrated therein the position of the parts after automatic opening of the circuit when the handle 23 is held in the on position. As will be seen from that figure, when the bimetal 6 has sufliciently cooled, portion 21 of spring 18 will engage the shoulder 28 provided in handle 23 to prevent the movable contacts return to closed circuit position. Release of the handle 23 from this position would cause counterclockwise rotation thereof under the influence of handle spring 20 whereby the parts will assume the position illustrated in Figure 2.

With the circuit breaker in the on position, should an increase in ambient temperature occur, main bimetal 6, which will flex in response to the heat generated by current flow therethrough and also in response to ambient temperatures, will tend to move toward the circuit opening position. In order to stabilize the current-time characteristics of the circuit breaker, the compensating bimetal 39 is provided which is affected only incidentally in response to current flow through main bimetal 6; however, upon increase in the ambient temperature, the legs of bimetal 39 will tend to diverge, whereby leg 42 of bimetal 39 will engage the main bimetal 6, applying a bias thereto which will tend to overcome that portion of the force developed in main bimetal 6 which is due to the higher ambient temperature. The point at which engagement of bimetals and opposition to movement occurs, and the amount of the opposition, will be determined by the value of the ambient temperature. Birnetal 39, however, is so chosen that it cannot prevent main bimetal 6 from moving the contact arm to the open circuit should overload current flow occur.

When the circuit breaker is in the on position and carries rated current, the temperature within the base 1 will increase sufficiently to cause the legs of compensating bimetal 39 to diverge slightly. Therefore, when main bimetal 6 is moved to off position under such circumstances, leg 42 of bimetal 39 will engage bimetal 6 and tend to urge it toward closed circuit position. Should the handle 23 be then returned to its on position immediately, this bias applied by bimetal 39 to bimetal 6 hastens the latters return to on position. As indicated above, the amount of divergence of the legs of bimetal 39, and therefore the degree of bias applied to main bimetal 6, is determined by the temperature to which bimetal 39 is heated.

It is obvious that the foregoing description of the operation applies to the constructions illustrated in Figures 1 through 7. The modification illustrated in Figures 6 and 7 has one additional feature. Figure 7 illustrates the stationary arc barrier 48 having an opening 49 therein through which the contact arm extends, and a movable arc barrier 51 mounted to the contact arm. Upon separation of the movable contact 9 from fixed contact 11, the movable arc barrier 51 is moved downwardly with the contact arm to impede passage of the arc drawn by the separation of the contacts through the opening 49 in the stationary barrier 48, and particularly to prevent roughing of the engaging surfaces of contact arm 43 and latch 44.

With respect to the embodiment of Figure 8, the circuit breaker operates as recited in the description relative to Figures 1 through 7, except that the handle cam directly engages the flange 17 on the armature plate 16, cam 25 applying a downward force to flange 16 to effect opening of the circuit breaker upon counterclockwise operation of the handle from the on position. With the parts in the off position, flange 17 directly engages the cam surface 27 of handle 23.

It will therefore readily appear that the circuit breaker of the present invention is one which accomplishes a quick-make and quick-break, trip-free action; in addition, the circuit breaker cannot reclose automatically regardless of handle position. These desirable effects are achieved at a very minimum of cost, with a minimum of parts, and without the use of an overcenter spring. It is further obvious that the circuit breaker of the present invention is compensated for undesirable ambient temperature changes so that the value of current which causes automatic opening of the contacts will be substantially the same regardless of increases in the surrounding temperature.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto, as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

What is claimed is:

1. In a circuit breaker, a fixed contact, a movable contact cooperating therewith to open and close the circuit therethrough, a contact arm carrying the movable contact, a bimetallic member carrying the contact arm and normally biasing the contact arm to closed circuit position, means for heating said bimetallic member in response to current flow through the breaker, said bimetallic member being positioned to flex when heated in a direction to move the contact arm toward open circuit position, a resilient U-shaped latch engaging the contact arm and opposing movement thereof to open circuit position until overcome by the force exerted by said bimetallic member upon current overload, manual means for forcing said contact arm past said resilient latch to open circuit position at will, and means on said manual means for preventing automatic return of said contact arm to closed circuit position after an automatic openmg.

2. In a circuit breaker, a fixed contact, a movable contact cooperating therewith to open and close the circuit therethrough, a contact arm carrying the movable contact, a bimetallic member carrying the contact arm and normally biasing the contact arm to closed circuit position, means for heating said bimetallic member in response to current flow through the breaker, said bimetallic member being positioned to flex when heated in a direction to move the contact arm toward open circuit position, a resilient U-shaped latch engaging the contact arm and opposing movement thereof to open circuit position until overcome by the force exerted by said bimetallic member upon current overload, manual means for forcing said contact arm past said resilient latch to open circuit position at will, said latch permitting return movement of said contact arm to closed circuit position under the bias of said bimetallic member without substantial opposition from the latch.

3. In a circuit breaker, a fixed contact, a movable contact cooperating therewith to open and close the circuit therethrough, a contact arm carrying the movable contact, a bimetallic member carrying the contact arm and normally biasing the contact arm to closed circuit position, means for heating said bimetallic member in response to current flow through the breaker, said bimetallic member being positioned to flex when heated in a direction to move the contact arm toward open circuit position, a resilient U-shaped latch engaging the contact arm and opposing movement thereof to open circuit position until overcome by the force exerted by said bimetallic member upon current overload, manual means for forcing said contact arm past said resilient latch to open circuit position at will, one leg of said latch having an inclined surface presenting a sharp edge past which one edge of said contact arm moves, the opposite leg of said latch presenting a substantially continuous, smooth surface along which the opposite edge of the contact arm moves.

4. In a circuit breaker, a fixed contact, a movable contact cooperating therewith to open and close the circuit therethrough, a contact arm carrying the movable contact, a bimetallic member carrying the contact arm and normally biasing the contact arm to closed circuit position, means for heating said bimetallic memher in response to current flow through the breaker, said bimetallic member being positioned to flex when heated in a direction to move the contact arm toward open circuit position a* resilient U-shaped latch engaging the contact arm and opposing movement thereof to open Circuit position until overcome by the force exerted by .said bimetallic member upon current overload, manual means for forcing said contact arm past said resilient latch to open circuit position at will, one leg of said latch having an inclined surface presenting a sharp edge past which one edge of said contact arm moves, the opposite leg of said latch presenting a substantially continuous smooth surface along which the opposite edge of-the contact arm moves, said latch permitting return movement of saidcontact arm to closed circuit position under the bias of said bimetallic member without substantial opposition from the latch.

5.. In .acircuit breaker, a fixed contact, movable contact. means movable to open and closed circuit positions, current responsive means normally biasing said movable contact means toward closed circuit position, said current responsive means operating to bias the movable contact means toward open circuit position upon the occurrence of a predetermined current overload a resilient latch engaging said movable contact means to opposemovement thereof to open circuit position until overcome by the force exerted by said current responsive means upon the occurrence of a current overload, manual means for moving said movable contact means past said resilient latch to open circuit position at will, and means movable with said current responsive means engaging the manual means to prevent automatic return of the movable contact means to closed circuit position after an automatic opening.

6; In a circuit breaker, a fixed contact, movable contact means movable to open and closed circuit positions, current responsive means normally biasing said movable contact means toward closed circuit position, said current responsive means operating to bias the movable contact means toward open circuit position upon the occurrence of a predetermined current overload a resilient latch engaging said movable contact means to oppose movement thereof to open circuit position until overcome'by the force exerted by said current responsive means upon the occurrence of a current overload, manual means for moving said movable contact means past said resilient latch to open circuit position at will, resilient means moving the manual means to oil? position after an automatic movement of the movable contact means to open position, and means movable with said current responsive means engaging the manual means to prevent automatic return of the movable contact means to closed circuit position after an automatic opening.

7. In a circuit breaker, a fixed contact, movable contact means movable to open and closed circuit positions, current responsive means normally biasing said movable contact means toward closed circuit position, said current responsive means operating to bias the movable contact means toward open circuit position upon the occurrence of a predetermined current overload a resilient latch engaging said movable contact means to oppose movement thereof to open circuit position until overcome by the force exerted by said current responsive means upon the occurrence of a current overload, manual means for moving said movable contact means past said resilient latch to open circuit position at will, resilient means moving the manual means to oil position after an automatic movement of the movable contact means to open position, and means movable with said current responsive means engaging the manual means when it is maintained in on position after an automatic opening to prevent automatic movement of the movable contact means to closed circuit position.

8. In a circuit breaker, a fixed contact, movable contact means movable to open and closed circuit positions, current responsive means normally biasing said movable contact means toward closed circuit position, said current responsive means operating to bias the movable contact means toward open circuit position upon the occurrence of a predetermined current overload a resilient latch engaging said movable contact means to oppose movement thereof to open circuit position until overcome by the force exerted by said current responsive means upon the occurrence of a current overload, manual means for moving said movable contact means past said resilient latch to open circuit position at will, resilient means moving the manual means to position after an automatic movement of the movable contact means to open position, and a second resilient latch movable with said current responsive means and moving into a position to engage the manual means when it is maintained in on position after an automatic opening to prevent automatic return of the movable contact means to closed circuit position.

9. In a circuit breaker, a fixed contact, movable contact means movable to open and closed circuit positions, current responsive means normally biasing said movable contact means toward closed circuit position and automatically moving said movable contact means to open position upon current overload, manual means movable to on and off positions to effect movement at will of said movable contact means to open and'closed circuit positions, the normal bias of said current responsive means being effective after an automatic opening of the circuit to return the movable contact means to closed circuit position unless opposed, and means engagea'ole with said manual means when said manual means is maintained in on position after automatic opening of the circuit to prevent automatic return of the movable contact means to closed circuit position.

10. In a circuit breaker, a fixed contact, movable contact means movable to open and closed circuit positions, current responsive means'normally biasing said movable contact means toward closed circuit position and automatically moving said movable contact means to open position upon current overload, manual means movable to on and off positions to effect movement at will of said movable contact means to open and closed circuit positions, means biasing the manual means to off position, means releasing the manual means for movement to off position under its bias upon the occurrence of automatic circuit opening, and means engageable with said manual means when maintained in on position after automatic opening of the circuit to prevent automatic return of the movable contact means to closed circuit position the normal bias of said current responsive means being prevented from-returning the movable contact means to closed circuit position by the normal engagement with the manual means in the off position after an automatic openingof the circuit or by the operation of said last mentioned engageable means when the manual means is maintained in on position after automatic opening of the circuit.

11. In a circuit breaker, a fixed contact, -movable contact means movable to open and closed circuit positions, current responsive means normally biasing said movable contact means toward closed circuit position and automatically moving said movable contact means to open position upon current overload, manual means movable to on and off positions to effect movement at will of said movable contact means to open and closed circuit positions, means biasing the manual means to off position, means releasing the manual means for movement to off position under its bias upon the occurrence of automatic circuit opening, and a resilient latch carried by said current responsive means and movable to a position to engage the manual means when main-- tained in on position after automatic opening of the circuit to prevent automatic return of the movable contact means to closed circuit position.

12. In a circuit breaker, a fixed contact, movable contact means movable to open and closed circuit positions, current responsive means normally biasing saidmovable contact means toward closed circuit position, a resilient latch engaging said movable contact means to oppose movement thereof to open circuit position until overcome by the force exerted by said current responsive means upon the occurrence of a current overload, manual means for moving said movable contact means past said resilient latch to open circuit position, resilient means moving the manual means to off position after an automatic movement of the movable contact means to open position, and a resilient latch movable with said current responsive means and moving into a position to engage the manual means when it is maintained in on position after an automatic opening to prevent automatic return of the movable contact means to closed circuit position, said last mentioned latch being engaged by the manual means in its movement from off to on position and moved against its bias to a position from which it is moved into closed circuit position under the bias of the current responsive means.-

13.- In a circuit breaker, a stationary contact, a movable contact cooperating therewith to open and close the circuit, a contact arm carrying the movable contact, a

bimetallic member carrying the contact arm and normallybiasing it to closed circuit position but flexing under current overload to move the contact arm to open circuit position, a resilient latch engaging the contact arm and opposing movement thereof to open circuit position, an operating handle, means biasing the handle to off position, an abutment carried by the bimetallic member, a recess in said handle receiving said abutment in the on position of the circuit breaker, and a surface on said handle engaged by said abutment in the off position of the handle to prevent automatic movement of the contact arm to closed circuit position.

14. In a circuit breaker, a stationary contact, a movable contact cooperating therewith to open and close the circuit, a contact arm carrying the .mc-vable contact, a bimetallic member carrying the contact arm and normally biasing it to closed circuit position but flexing under current overload to move the contact arm to open circuit position, a resilient latch engaging the contact arm and opposing movement thereof to open circuit position, an operating handle, means biasing the handle to off position, an abutment carried by the bimetallic member, a cam surface on the handle engaging said abutment to retain the handle in normal on position against the bias of said means, said abutment releasing that handle for movement to off position under its bias upon automatic movement ofthe contact arm to open circuit position, said abutment engaging the handle to prevent automatic return of the contact arm to closed circuit position when the handle is in off position.

15. In a circuit breaker, a stationary contact, a movable contact cooperating therewith to open and close the circuit, a contact arm carrying the movable contact, a bimetallic member carrying the contact arm and normally biasing it to closed circuit position, means for heating said bimetallic member in response to current flow through the breaker, said bimetallic member being positioned to flex when heated in a direction to move the contact arm toward open circuit position a resilient latch engaging the contact arm and opposing movement thereof to open circuit position, an operating handle, means biasing the handle to off position, an abutment carried by the bimetallic member, a spring strip mounted on and spaced from said abutment so as to present a resilient engaging surface, a cam surface on said handle engaging said resilient surface in the normalon position of the handle, said spring strip being stressed to incline said resilient surface relative to the cam surface as the handle is manually moved toward off position to facilitate moving the contact arm past the latch into open circuit position.

16. In a circuit breaker, a stationary contact, a movable contact cooperating therewith to open and close the circuit, a contact arm carrying the movable contact, a bimetallic member carrying the contact arm and normally biasing it to closed circuit position, means for heating said bimetallic member in response to current flow through the breaker, said bimetallic member being positioned to flex when heated in a direction to move the contact arm toward open circuit position a resilient latch engaging the contact arm and opposing movement thereof to open circuit position, an operating handle, means biasing the handle to off position, an abutment carried by the bimetallic member, a spring strip mounted on and spaced from said abutment so as to present a resilient engaging surface, a cam surface on said handle engaging said resilient surface in the normal on position of the handle, means biasing said handle toward off position, said cam surface and resilient surface being undercut with respect to a radial handle plane to prevent involuntary handle movement to off position under its bias, said spring strip being stressed to incline said resilient surface relative to the cam surface as the handle is manually moved toward off position to facilitate moving the contact arm past the latch into open circuit position.

17. In a circuit breaker, a station contact, a movable contact cooperating therewith to open and close the circuit, a contact arm carrying the movable contact, a bimetallic member carrying the contact arm and normally biasing it to closed circuit position, means for heating said bimetallic member in response -to current flow through the breaker, said bimetallic member being post-- tioned to flex when heated in a direction to move the contact arm toward open circuit position a resilient latch engaging the contact arm .and opposing movement thereof to open circuit position, an operating handle, means biasing the handle to off position, an abutment carried by the bimetallic member, a spring strip mounted on and spaced from said abutment to present a resilient engaging surface, a cam surface on the handle engaging said resilient surface to retain the handle in normal on position against the bias of said means, said spring strip having a double return bend, one extreme leg of said strip constituting said resilient surface, the opposite extreme leg constituting a resilient latch engaging the handle when it is maintained in on position after automatic opening to prevent automatic return movement to closed circuit position.

18. In a circuit breaker, a stationary contact, a movable contact cooperating therewith to open and close the circuit, a contact arm carrying the movable contact, a bimetallic member carrying the contact arm and normally biasing it to closed circuit position, means for heating said bimetallic member in response to current flow through the breaker, said bimetallic member being positioned to flex when heated in a direction to move the contact arm toward open circuit position a resilient latch engaging the contact arm and opposing movement thereof to open circuit position, an operating handle, means biasing the handle to off position, an abutment carried by the bimetallic member, a spring strip mounted on and spaced from said abutment to present a resilient engaging surface, a cam surface on the handle engaging said resilient surface to retain the handle in normal on position against the bias of said means, said spring strip having a double return bend with one extreme leg constituting said resilient surface and the opposite extreme leg constituting a resilient latch engaging the handle when it is maintained in on position after automatic opening to prevent automatic return movement to closed circuit position, and a recess in said handle receiving said double return bend in the normal on position of the breaker parts, one side wall of said recess constituting said handle cam surface, the opposite side wall engaging said extreme spring strip leg as the handle is moved from off to on position to stress the leg so that the double bend will be received within the handle recess.

19. In a circuit breaker, a stationary contact, a movable contact cooperating therewith to open and close the circuit, a contact arm carrying the movable contact, a bimetallic member carrying the contact arm and normally biasing it to closed circuit position, means for heating said bimetallic member in response to current flow through the breaker, said bimetallic member being positioned to flex when heated in a direction to move the contact arm toward open circuit position a resilient latch engaging the contact arm and opposing movement thereof to open circuit position, an operating handle, means biasing the handle to off position, an abutment carried by the bimetallic member, a cam surface on the handle engaging said abutment to retain the handle in normal on position, manual movement of the handle to off position causing said cam surface to move the abutment and force the contact arm past the latch into open position, and resilient means engageable by the handle when manually moved past its on position to apply a bias to the contact arm substantially equivalent to the bias applied thereto by the handle bias through the cam surface and abutment when the handle is in normal on position.

20. In a circuit breaker, a fixed contact, a movable contact cooperating therewith, a contact arm carrying said movable contact, a current responsive bimetallic strip normally biasing said contact arm toward closed circuit position but flexing when heated to move the contact arm to open position, a resilient latch normally opposing movement of said contact arm to open position until overcome by the flexing force of the bimetalilc strip, a second bimetallic strip positioned to flex in a direction opposite to the flexure of said first bimetallic strip, said second bimetallic strip being responsive to the same ambient temperature as the first bimetallic strip but not current responsive and positioned to engage the 11 first bimetallic strip upon increase in ambient temperature to "oppose flexure thereof.

21. In a circuit breaker, a fixed contact, a movable contact cooperating therewith, a contact arm carrying said movable contact, a current responsive bimetallic strip normally biasing said contact arm toward closed circuit position but flexing when heated to move the contact arm to open position, a resilient latch normally opposing movement of said contact arm to open position until overcome by the flexing force of the bimetallic strip, a second bimetallic strip positioned to flex in a direction opposite to the fiexure of said first bimetallic strip, said second bimetallic strip being responsive to the same ambient temperature as the first bimetallic strip but not current responsive, said first strip being spaced from said second strip at normal ambient temperature when the contactsare engaged and flexing under increased ambient temperature to engage the second strip and oppose contactopening fiexure thereof with a force varying with the ambient temperature whereby to com- 20 pensate for the effect of ambient temperature on the calibration of the circuit breaker.

22. In a circuit breaker, a fixed cor'itac't, a movable contact cooperating therewith, a contact arm carrylng said movable contact, a current responsive bimetallic strip normally biasing said contact arm toward closed circuit position but flexing when heated to move the contact arm to open position, a resilient latch normally opposing movement of said contact arm to open position until overcome by the flexing force of the bimetallic strip, a second bimetallic strip of substantially U shape, with the high expansion metal on the inside of the U, disposed on the low expansion side of the first strip with one leg of the U anchored and its free leg positioned to apply a bias to the first strip as the ambient temperature increases so as to compensate for the effect thereof on the fiexure of the first strip.

References Cited in the file of this patent UNITED STATES PATENTS Name Da 

